The quality of foods, drinks, drugs and the like is deteriorated by oxygen, and therefore they are desired to be stored in the absence of oxygen or under the condition with an extremely small amount of oxygen.
Accordingly, containers or packages storing foods, drinks, drugs or the like are often purged with nitrogen. However, the method is problematic in that, for example, the production cost may increase and, when they are once opened, air may flow into them from the outside and thereafter the quality deterioration could be no more prevented. Therefore, various investigations have been made for absorbing oxygen remaining in containers and packages and moving oxygen from them.
Recently, for resin containers or packaging materials, there has been mainly employed a method of making a resin container or a packaging material itself have oxygen absorbability.
As an oxygen absorbent for producing such oxygen-absorbing containers, for example, there is proposed an oxygen absorbent that comprises a polyterpene such as poly(α-pinene), poly(β-pinene) or poly(dipentene) (Patent reference 1), a conjugated diene polymer such as polyisoprene or 1,2-polybutadiene (Patent Reference 2), a copolymer of ethylene and cyclopentene (Patent Reference 3), a styrene-diene copolymer and/or a hydrogenated styrene-diene copolymer (Patent Reference 4) or the like, and a transition metal salt serving as an oxygen absorption catalyst such as cobalt neodecanoate or cobalt oleate.
However, these conventional oxygen absorbents are often difficult to use in some applications since the polymer may be deteriorated with the advance of oxygen absorption reaction and their mechanical strength may significantly lower or the transition metal compound such as a transition metal salt may bleed out.
Patent Reference 1: JP-T 2001-507045
Patent Reference 2: JP-A 2003-71992
Patent Reference 3: JP-T 2003-504042
Patent Reference 4: JP-A 2005-15055
The present inventors have noted a cyclized product of a conjugated diene polymer as an oxygen absorbent free from the above-mentioned problems, and have made studies of its application. Differing from the above-mentioned conventional oxygen absorbents, a cyclized product of a conjugated diene polymer has the advantage of exhibiting its excellent oxygen absorbability even in the absence of a catalyst metal compound.
The inventors have found an oxygen-absorbing resin composition that comprises an oxygen-absorbing resin (A1) having a cycloene structure in the molecule and a softener (A2) and has a glass transition temperature of not higher than 30° C., as an improvement on the cyclized product of a conjugated diene polymer in point of the oxygen absorbability at room temperature (Japanese Patent Application No. 2006-039044).
However, it could not be said that there may be no further room for improving the oxygen-absorbing resin composition in point of the level of bad smell to be released on oxygen absorption.